[CentOS] mdraid Q on c6...

Sun Jun 22 08:15:23 UTC 2014
John R Pierce <pierce at hogranch.com>

so, I installed a c6 system offsite today, had to do it in a hurry.   
box has 2 disks meant to be mirrored...  I couldn't figure out how to 
get anaconda to build a LVM root on a mirror, so I ended up just 
installing a /boot and vg_system on sda and raid it later.

every howto I find for linux says to half-raid the OTHER disk, COPY 
everything to it, then boot from it and wipe the first disk and then 
bond it as a mirror of the 2nd.   Thats kind of ugly.

in solaris, you can tell it that your existing partition is half of a 
mirror, update /etc/vfstab, then reboot, and then join a mirror to it.   
this seems much cleaner to me than copying everything.

I tried to do this the solaris way, and at the first step, am told...

    # mdadm --create /dev/md0 --level=mirror --raid-devices=2 /dev/sda2
    mdadm: cannot open /dev/sda2: Device or resource busy

/dev/sda2 contains the LVM root vg...

so... I'm thinking I''ll boot a rescue system from usb, create the half 
mirror, then reboot to the incomplete raid and add mirror /dev/sdb2

will the VG be found on /dev/md0 instead of on /dev/sda2 ?
if so, is there any other reason this won't work?

john r pierce                                      37N 122W
somewhere on the middle of the left coast